440-22A piston skirt blowout

[eppjd]

Allow me to explain...

Out on my '75 800 the other week, first ride of the season after sitting all summer with tank filled with mixed fuel and stabillizer. Started good as always (started couple times through the summer to keep the carb wet) and warmed it up a bit before I headed out. Deep powder and fairly tough going till I got way out, after about 3 miles my engine locked up. Tore the heads off to discover aluminum fragments on top of piston 2 (left, clutch side), must have dislodged one piece out of the exhaust port because then the engine would turn freely. Only damage I can see at this point is the skirt blown out of the piston. Has anybody experienced this before and what did they diagnose as the cause. It did not even score the bore, not a scratch, and the head looks good as well.

Overall not too bad considering I thought I melted the whole thing down.

As a side, what kind of a hone would I use to go through the bore? Just as a precaution I thought I would hone both cylinders before reassembly.


Thanks for any input,
Adam

[JDT]

Adam if the skirt broke off it fell down into the crank and was ground up into small enough pieces to go though the tranfer ports and then lock up the motor.

There may not be any visable damage on the top end but the crnak may be a mess.

Little pieces of skirt in your bearings, ect.

Do a complete engine tear down and cleaning followed by a very carefull bearing inspection.

[S_Kyle]

Todd, we will be dong a complete tear down. The motor is sitting in my garage. But what actually causes a piston skirt failure? I understand that the motor was rebuilt not to may miles ago with new +.010 pistons, gaskets, etc. I can't say I have seen a piston break is skirt before and kind of wonder why. I might go snap a pic if I get ambitious today.

[JDT]

What causes a skirt to break I do not know. But I have seen it a few times.
You will likey find some serious issues in the lower part of the engine.

[S_Kyle]

I hope not, but at least I have anouther crank we can use if we have too. I hope to have time to check out the problem myself tomorrow between games, local bonspiel on this weekend.

[JDT]

I have even seen a chunk of skirt sticking out through the bottom case half.
Counterweight came around and blew it right out.

[JD_Sledder68]

They didn't go .010 over on the bore and then put standard pistons back in that motor did they?

[eppjd]

Good question, I never measured the pistons. I will check that thanks.